How to freeze drying/lyophilize fruit?
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How to freeze drying/lyophilize fruit?
Publisher:   Source:   Date:2017-05-23   Clicks: 
How to freeze drying/lyophilize fruit?
Freeze dried fruits is required to use freeze drying technique/lyophilization to dehydrate fresh fruits. The principle of freeze drying is a process to quick freeze internal water of fruits, then removing the water directly from ice to vapor by sublimation. According to freeze drying principle, we got to know that the freeze drying machine must be equipped with the ability to quick freeze, we have to note that it is quick freeze rather than simply freeze, because the quick freeze would request much lower temperature that can make the internal water of fresh fruits quickly freeze into small ice crystal, and quick freeze can prevent forming big ice crystal which would destroy the internal structure, leading to less ideal quality of finished freeze dried fruits. Freeze dryer must also be equipped with vacuumizing function, the lower the pressure is, the lower the ice sublimation temperature is. Fruit freeze drying machine also asked for heating function, because ice sublimation needs to absorb heating, moderate heating can speed up the sublimation.
It is suggested to choose a set of efficient and reliable fruit freeze dryer before starting to freeze drying fruits. Fruit freeze dryer is quite different from pharmaceutical freeze dryer, medicine especially the injection medicine which has strictly operational process and hygienic regulation. Fruit freeze drying equipment is over qualified to meet food level sanitary requirement. The following steps show how to freeze drying fruits?
  1. Preparing fresh fruits, then cleaning, peeling, dicing or slicing the fruits.
  2. Putting the prepared fruits on trays, and then inserting the sensors into fruits to start pre-freeze.
  3. Quick freezing fruits up to fruit internal completely frozen
  4. Refrigerating vapor condenser, it is used to collect vapor from fruit.
  5. Vacuumizing while the temperature of vapor condenser reach -40 ℃.
  6. Heating fruits while the vacuum level is under 50pa.
During this process, water is removed from fruits by sublimating from ice to vapor step by step, at the same time; vapor is caught by vapor condenser congealing on the coil pipe. The fresh fruit is totally dry after removing all the water. Some companies make the defrosting happen by electrical heating simultaneously with the above process, which would slower the speed of catching water and fall short of saving time, while increasing the energy consumption, so it is not widely used.
When product temperature and pre-set temperature is the same, meanwhile vacuum level reached unloaded ultimate vacuum, all these conditions represent products is already freeze dried. Now you can shut down freeze dryer and release pressure, then unload freeze dried fruits and pack them promptly. The freeze dried fruit would not lose any nutrients except water, and freeze dried fruits is fluffy and porous and there is no change in size and shape. After freeze drying, the freeze dried fruits is more sweeter, more fragrant and more crispier. There is no need to use additive, pigment and preservative during processing and packing. Simple sealed package can preserve freeze dried fruits for at least 2 years. With the improvement of living standard, this natural and healthy freeze dried fruit crisp will be more and more welcomed by consumers. It is an ideal investing project for the short-season and high nutrient fruits.
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